Amplifying system



Feb. 5, 1952 J. LONGO ET AL 2,584,213

AMPLIFYING SYSTEM Filed May 1, 1950 *,Z j@ f Patented Feb. 5, 1952 AMPLIFYING SYSTEM John Longo and Simeon I. Tourshou, Philadelphia, Pa., and Robert J. Lewis, Audubon, N. J., assignors to Radio Corporation of America, a corporation of Delaware Application May 1, l1950, Serial No. 159,354

The present invention relates to high efficiency electronic power amplifying systems, `and more particularly although not necessarily exclusively, to such systems in which the electron discharge tube employed as an amplier is made conductive for only a portion of the period of the signal excursion applied to the tube.

More particularly the present invention relates to high eii'iciency power amplifiers of the type used in present-day electromagnetic beam deflection circuits as, for example, found in television receivers.

As is well known by those skilled in the electronic art, the power efficiency of signalampliers can be made increasingly higher by reducing the duty cycle of the electron tube involved. The lowest eiiiciency amplifier type is the class A amplifier in which plate current flows in the electron tube continuously. The signal applied to the ampliiier operates on a linear part of the tube characteristic to produce a very faithful amplification of the signal. Class B" type signal amplifiers are usually found in push-pull type systems where each tube, although statically conductive is driven into high current conduction by opposite polarity excursions of the applied` signal. The eiiiciency is thus made higher, but the fidelity, unless extreme care is taken, may suffer. In class C type amplifiers, fidelity is of no importance and power eiiiciency is of sole concern. Here, the applied signal causes the class C ampliiier type to conduct only for a very small portion of the signal period.

A form of the class C amplifier is today used in commercial television deection systems. For example, in an electromagnetic beam deflection system a saw-tooth of voltage is applied to the grid of a power amplifier tube. If reaction scanning techniques are employed, the amplifier tube need conduct only 'for a little over half of the total saw-tooth period. The remaining sawtooth of deflection current in the electromagnetic yoke is, as well known in reaction scanning systems, supplied by a damping tube which captures and puts to work the stored magnetic energy in the yoke. However, as the cathode ray tube screen areas of television receivers become greater, more and more power is required to successfully deflect the electron beam.

Thus, in order to reduce the cost of deflection power amplifiers, an effort has been extended to increase the efficiency of deflection power arnplier circuits so as to get the required increased deflection with presently available low cost, lowerr power tubes.

It is,` therefore, a purpose of the present 1nvention to provide an improved mode-'ofopera-t-f ing electron discharge tubes so vas to increase their effective power handling capabilities.

It is a further purpose of the present invention to provide a signal control systemA for class -C"- type ampliers whichv will considerably increase". their power handling abilities. f v

It is a still further purpose ofthe present in vention to provide an improved powery amplifier circuit for electromagnetic cathode ray-'beam deflection whereby additional useful deiiectionv may be obtained from existing power amplifier tubes having limited power handling abilities.

In realizing the above advantage, the present invention, as applied for example to classl .C"*. type amplifiers using screen grid tubes, contemplates the followingv arrangement. A special control signal is generated'whose frequency is equal to lor an integral multiple of the signal, frequency being handled by the power amplifier. The phase and wave form of this signal is so adjusted that when applied to the screen elec.- trode of the power tube the screen grid electrode is swung negatively during non-conductionoff the discharge tube and swung positively duringy the conduction of the discharge tube. Thus where the load circuit of the amplifier -tube is of the oscillatory type, such as found in Velectromagnetie deiiection systems, considerablevincrease ,inv power output is gained. This is caused since .during cut-olf the tube is further disabled by' the invention from conduction by the negative',V excursion of the screen. This prevents any possible unwanted damping of load circuit signals` by the anode-cathode path of the tube. Drilling conduction, however, the screen grid receives ar positive-going excursion which increases the am- K plitude of powerr tube anode current above that' otherwise obtained.

i Other objects, features and advantages in addition to those set forth herein above, as, well as a more complete understanding of the present invention will appear from a reading of the 'fol-L, lowing speciiication especially when vtaken in combination with the following drawings f' in' which: Q

Figure 1 is a combination block diagramfandju schematic representation of one form of the invention as applied to a typical electro-magrietic system for a television receiver.

Figure 2 is a'combination block diagram and" schematic representation of yet another embodi'` ment of the present invention useful for' application in electromagnetic cathode ray beam deflection systems. Y

Turning now to Fig. 1, there is indicated at Il! demodulated signal is also applied to a sync sepa rator circuit shown at I 6. The outputtofthe sync separator is then applied for synchronizing a horizontal deflection generator IE aswelll as' Gen eral ly,v thea vertical deflection circuit atfZD; signal wave form appearing'atthe output ofthe signal generator I8 is of saw-tooth form shown for example at 22. for the block representation of the televisionreceiving circuit elements I D through are'shov/nv and discussed in an article entitled Television Receive-rsi. by." Antony:v Wright appearing' in the Review for ltlarcln194W".l

The-output: of? the horizontal'y deflection signal generator: is-l applied: to someL form of? electron dischargei-amplifying-tube such as illustrated at shown as a pentode-type t'ube.- The d'eection signal 22 l is applied tothe control grid 2 Si o1Y the tubee The-suppressor ygrid 2T is connected with th'el-cathode. Screen gridz' is positively biased withv respect'to'thecathode-3D by means of its connection tothe positive power supplypterminal 32. The anode'34 ofithepentode 24 may be provided'with'- any form ofload-circuit for coupling with theb deflection yoke Windingfat 36. AY numberfof suitable deilection circuits which may be connected with the anode ofthe tube 24 are shovvrrandI discussed in an article 'entitled Television; Deflection Cir.cuits."byA. WI Eriend'appea-ring in the'RCA Review Vfor March 194'7. Another article entitled Magnetic Deflection Cir.-

cuitsior; Cathode R'ay`Tubes'by OttoH. Schade.

appearingjin the'RCA Review'for September 1947 discusses even. other typical electromagnetic. deflction circuits suitable for. connection with the anode ofgpentode 24.

The .particular de'ection circuit. shown.in

Lisofjthedirect drive variety; That is, onein which thedeflectionyoke Winding 39 is directly connectedas partcfithe anode-cathode loadLcircuit ,of."the,pentode24. As noted above, this cir,- cuitlis, .oi course,.exemplary andmay be replaced. as, far.. as; the ,present4 invention is concerned by any, type of.,deection system.

Themarticular, directdrivesystem shown in Fig. ,l comprisesv a; connection .from the., anode.. 34A tothe..p rimary,. of a highivoltagepulse. step-up transformer 31; appearing., across;` the. secondary,v 3,8A are rectied bythediOde. 40top roduce .beam-.accelerating p o tential for,the.kinesco.p,e 42.` The lowenextremity.

cnthegwinding 3.1Y is then .connectedlwiththe horizontal deflection .yoke` winding. 36of.. the yde- 'ectionfyoke.. Fromthe lower end ofQthe deflection yoke winding a capacitor 44 is connectedlto. the, upper. end. of ,thetransformer primary 4S. The lower extremity.r of. the transformer. primary. 462isfconnectedto thefpower supply terminal A32. An additional capacitor;` 48 Iisfccnnected fromthe lower endofthefwinding: 36 the positive-power supplyfterrrlinai'32'1'l Detailed description -of hovv` this circuit` operatesl mayrbe. found in` thel Radio Co'rporationY of America ServicelNotesf on Telee vision Receiver Models T-164, TC 166,'TC'167', TC

168,1rstfe'dition datedfMarch 10319502" The par- Examples of suitablev circuits Resulting positiveegoing, pulsesV ticular direct-driveV circuit shown is also more fully described in co-pending U. S. patent application Serial No. 90,612, led April 30, 1949, by Simeon I. Tourshou entitled Television Delection Power Recovery Circuits, Patent No. 2,555,831, granted June 5, 1951.

Briefly, the, discharge tube 24:; is'. biased by means of the bleeder resistor 50 connected from the positive source of supply 52 to the cathode 3i! Yofthe output tube. The resulting voltage drop acrossthecathode resistor 54 biases the tube so that under normal operating conditions the tube conductsonly-fduring'v'the positive-going extremitiesof thesa'W-'toothf22- This causes a saw-tooth of; current. flowto; start building up in the yoke Winding 36. As soon as the retrace portion of tliexsaW-toothxoccurs an oscillatory ringing starts inv the. deflection yoke Winding 36. This is damped' by the diode 49 to cause a saw-tooth of current to start flowing'in the yoke 35 in the opposite-direction. By properlyadjusting tlie= bias cnt the tube24'and'= the'- amplitude oi the-signal? 22;v a quite linear' saw-toothI ofv current'- suitablefor deilection` purposesY may be produced throughtheY yoke winding" 36".

However, according to the-embodiment offthe present invention shown inl Fig. 1, thesecondary` 56 of the transformer 41 is connected in series with. the circuit `path betweenl the positive Apower 'supplyl terminal 32 and tliescreenl grid 28; Al

signal Wave form on` the screen grid'ZB- vvhichisn basically sinusoidal in form but. having some irregularitiesdue to .the saw-tooth*drive.4 By-Way of example, suchlavfaveA forrrrmayn appear like` thatshownat. 60.

In the operation'of thepresentinventionlthc, phase 'of .the Wave form=6 fisso. adjusted that .the screen grid 28v` swings positively duringconduc.- tion ofthe .pentode 24. On,the,otherhand. Idur.-

ing non-conduction. of. the pentode 2.4 .the screen.

A:28,--ismade tolsWing negatively. The negativegoingr swing duringv cutfoff.. of.A the tubemendersfthe.anodecathode path.v of: thetube.; a-..ver.y high impedance. Thisvpreventsl any-` magnetic energy in the-deflection. system from being. wastedacross res-idualanode-cathode resistance of. the output tube. On the other hand, sincethe screen-ismade to swing positively;` inaccordance` Withlthe present-invention, during conductionot the output'tube, a much higher pov/erl outputy from theV tube is made possible. Since this-higher` screenv voltage is only'effectiveforibut-.abriet period, the average screen `dissipationnf ythe.tubeis.-kepty low. Byf properly proportioning the -control l signal 60A applied' to thei screen',-r an` increasefz ini deflection amplitude of 20 -to A3.0:percent over any; presently known prior art'. arrangement maybe l achieved Without-1 unduly burdeningV the tube 'l 2 4 t The way in which the'control-signal 60A is appliedto the vscreen, of ithe cutput'tubeis notfof too ment shown in Fig: Zshovvsav simplified formD of' thev present: invention'. As' inspectiony willf show, the general' directed'rive deiiectionl circuitoff. Fig:

2 is the same asthatshownin Fig; 1T and: like components have been givenv simil-ar4 reference numerals. However; in Fig. 2; insteadof developing the control signal by means of atransformerVV responsive" to1 current? variations' in':V the output circuit of the tube 24, the control voltage is developed simply by shock excitation of a tuned circuit. In Fig. 2, therefore, the screen 28 is connected with the positive power supply terminal 32 through a given inductance 62. The dropping resistor 64 by-passed by capacitor 66 may be employed to adjust screen potential if desired. In Fig. 2, however, the capacitor 68 is selected in value to form a tuned circuit with the inductance l62. As in Fig. l, thefrequency of this resonance may be either equal to the deiiection rate of the system or a harmonic thereof. The resulting control signal 60' superimposed on the positive bias of the screen 28 will act as described in Fig. l to increase the eiciency of the amplifying stage. In Fig. 2, the proper bias for the discharge tube 24 is obtained not through a cathode bleeder system as in Fig. l but through a combination grid leak bias and cathode bias arrangement. Grid leak resistor 'le connected from the grid 26 to ground is selected in value to obtain the requiredbias conditions.

Although the present invention has been described in connection with a pentode-type amplifier tube, it is apparent that other multi-grid type tubes may be substituted therefor Without departing from the spirit and scope of the present invention. Furthermore, although particular attention has been directed to deflection type class C amplifiers, it will be clear that amplifiers for purposes other than deflection may take advantage of the improvement provided by the present invention.

Having thus described our invention what is claimedis:

l. In an electro-magnetic cathode ray beam deflection system adapted for excitation of a beam deflection yoke, a combination of a source of deflection signal having a predetermined frequency, an electron discharge tube having at least an anode, cathode, a first control electrode and a second control electrode, connections for applying the output of said deection signal source to said first control electrode of said discharge tube, an output circuit connected between the anode and cathode of said discharge tube, circuit means for exciting the deflection yoke with energy developed in said output circuit, means connected between said second control electrode and said cathode for biasing said second control electrode positively with respect to said cathode, a source of substantially sinusoidal control signal having the frequency and phase thereof related to said deflection signal frequency in a predetermined manner, and means for super-imposing said control frequency upon the positive bias applied to said second control electrode.

2. Apparatus according to claim l wherein said deiiection signal source is productive of a substantially saw-tooth wave form.

3. Apparatus according to claim 1 wherein said source of control signal comprises means for generating an electrical signal in accordance with current iiow in the output circuit of said discharge tube.

4. In an electrical signal amplifying circuit, the combination of a source of signal voltage, an electron discharge tube having at least an anode, cathode, a rst control electrode and a second control electrode, said second control electrode being adjacent to said rst control electrode but more remote from said cathode than said first control electrode, means for applying the output of said signal source between the iirst control electrode and cathode of said discharge tube,`

means for negatively biasing said rst control electrode relative to said cathode such that said discharge tube is conductive for only a portion of the wave form defined by said signal source, an output circuit for said discharge tube connected between said anode and said cathode, means for biasing said second control electrode positively with respect to said cathode, a source of control signal having a frequency which is an integral multiple of said signal voltage, and means for super-imposing said control signal upon the positive Vbias applied to said-second control electrode.

5. Apparatus according to claim 4 wherein saidv source of control signal comprises means coupled with said output circuit for developing an elec' trical waveform in accordance with current variations in said output circuit.

6. Apparatus according to claim 5 wherein th waveform and phase of said control signal is so determined and related to said signal voltage and first control electrode bias that said second control electrode is swung in a negative direction during non-conduction of said discharge tube and in a positive direction during conduction of said discharge tube.

'7. An electron ray beam deflection system ernploying a deflection yoke having deiiection winding terminals, the combination of a source of deflection voltage having at least a saw-tooth component, an electron discharge tube having at least an anode, cathode, control electrode and screen electrode, means for applying said deflection signal between the control electrode and cathode of said discharge tube, means for biasingr said control electrode relative to said cathode such that said discharge tube is rendered conductive only during a positive-going portion of said deflection signal, an output circuit connected between said discharge tube anode and its respective cathode, said output circuit including means for positively biasing said anode relative to said cathode, means connected with said output circuit and said deflection yoke winding terminals for exciting said yoke from energy developed in said output circuit, means for generating a substantially sinusoidal control signal having a frequency which is an integral multiple of the deiiection signal frequency, means for biasing said screen electrode positively with respect to said cathode, and means for super-imposing the said control signal on the positive bias applied to said screen electrode.

8. Apparatus according to claim '7 wherein said means for generating a control signal comprises a parallel tuned circuit serially connected between said screen electrode and said biasing means for said screen electrode.

9. Apparatus according to claim 7 wherein said means for generating a control signal comprises a transformer having a primary and secondary winding, said primary winding being connected with said output circuit for excitation thereby while one terminal of said secondary winding is coupled with said screen electrode and the other terminal of said secondary winding is coupled with the end of said primary winding adjacent the cathode of said tube.

10. In an electrode-magnetic cathode ray deiiection system of the direct drive type which employs a deflection yoke having two utilization terminals for energizing the complete yoke deflection winding, said deflection yoke utilization terminals being serially connected in the anodecathode circuit of a screen gridoutput vacuum tube'amplier, the combination of, a first capacitorconnected kin series with said deection coil terminals in the vacuum tube amplifier anodecathode circuit, a transformer having a primary and a'secondary winding, a second capacitor connected in series with said transformer primary winding to form a combination, eonnectionsplacing said combination in .shunt with a portion of the' amplier anode-cathode circuit which includes said first capacitor, a unilaterally conduce tive damping device connected in shunt through at least'a portionof said transformer lprimary winding With a portion of said vacuum tube amplier lanotie-cathode circuit, anda connection from the screen Ygrid of said Vacuum tube amplierthrough said. transformer secondary Winding toa source of positive potential.

11.1.1.1 an electro magnetic cathode'vray deflection system o'f the direct drive type which ernploys 1a Ydeflection yoke having two utilization terminals for energizing the'complete yoke deflee-tion winding, said deflection yoke utilization terminals being serially connected in the anodecathode circuit of a'screen grid Vacuum tube amplier, the combination of,a first capacitor'connectecl in series with said deection coil terminals in the vacuum tube amplier anode-cathode circuit, an `inductance and second capacitor connected in series with one another to form a combination,.connectionsplacingsaid-inductance and capacitor combinationin shunt Withla portionoffthe amplier anode-cathode circuit Awhich includes said rst capacitor, a unilaterally conductive clamping device vconnected in shunt through. at least aportion of said inductance withv a yportion of said output amplier anode-cathode circuit, and a second inductance connected from4 thescreen-grid of said vacuum tube amplifier .to asource of positive potential.

' JOI-IN LONGO.

SIMEON I. TOURSI-IOU. ROBERT J. LEWIS.

REFERENCES CITED The following references are of record in the le-ofthis patent:

`UNITED STATES PATENTS 

